In many situations, it is desirable to selectively transmit light in order to limit visibility of a light source to certain observers.
For example, some vehicles, such as motor vehicles, are equipped with a display device, such as a TV, video player, gaming device, dashboard display, or the like. Display monitors are now commonly mounted inside automobiles for viewing by occupants. For various reasons such as safety and privacy, it is sometimes desirable to limit the visibility of the displayed image through a vehicle window, so that an observer outside the vehicle such as another road user cannot see, or clearly see, the displayed image.
In a further example, automated teller machines (ATMs) are typically equipped with a display for viewing by a user. For privacy reasons, it is desirable to limit the visibility of the displayed information to a bystander.
Additional examples of the light source include computer monitors, televisions, video players, gaming devices, and control panels.
A known technique utilizes a pair of linearly polarized films to limit the visibility of a dashboard display device through the rear window of a vehicle. One of the two films is placed on the display device and the other is imbedded in the rear window. The transmission axes of the two films are nearly at a right angle. As a result, a beam of light can pass through one film but not both films. Thus, the display device is visible to an occupant of the vehicle but almost invisible to the driver in a succeeding vehicle.
However, such a technique has some drawbacks. For instance, problems can arise when an occupant wears polarized eyewear, which is common for mitigating sunlight glare. Lenses of the polarized eyewear can block the linearly polarized light transmitted through the rear window, or from the display. The occupant may have trouble viewing the display or seeing the outside through the rear window. This can be inconvenient. Worse still, if the occupant is the driver, accidents can occur due to the impaired rear-view vision.
Accordingly, there is a need for an improved technique of controlling light transmission, such as for limiting visibility of a display from a selected region around the display.